This application is based on Application No. 10-76866 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a distance detecting device for detecting the distance to a photographic subject for use in a camera, video camera, still video camera and the like.
2. Description of the Related Art
Distance detecting devices of the passive type used in cameras and the like condense light via a pair of optical systems to condense the light flux from a photographic subject, and form images on a pair of image sensors such as an area sensor or the like arranged in the rear of the optical system. Information expressing luminance distribution of a specific area on both image sensors is extracted to detect the distance to the photographic subject from the difference in the extracted luminance distributions via the principle of trigonometric survey.
When using the aforesaid method under low contrast conditions, however, the reduced distance detection accuracy results in inaccurate measurement. In order to eliminate this problem, methods have been proposed for increasing the area of the image on the image sensor from which the image information is extracted so as to enable distance detection of a photographic subject under low contrast conditions.
When this method is used in a camera, it is possible to accurately measure distance of a photographic subject under low contrast conditions by, for example, orienting the photographic plane 1 with the vertical length, and enlarging the area of a region (hereinafter referred to as the xe2x80x9cmeasurement regionxe2x80x9d) 2 used for distance detection on the image sensor corresponding to the photographic plane 1, as shown in FIG. 1A. However, the measurement region 2 may be set as the horizontal length when the photographic plane 1 is oriented in the horizontal direction by changing the orientation of the camera, as shown in FIG. 1B.
With this method the distance measurement accuracy is reduced when the background 4 outside of the photographic subject 3 within the photographic plane 1 intrudes into the measurement region 2, and the luminance distribution information of the non-photographic subject region is also used in the distance detecting calculation. Even if the photographic plane 1 is set in the horizontal direction and the measurement region 2 is set in the vertical length, when the photographic plane 1 is set in the vertical direction, a similar disadvantage arises since the measurement region 2 is horizontal length.
An object of the present invention is to improve the distance detection accuracy relative to a photographic subject under low contrast conditions.
Another object of the present invention is to provide a distance detecting device which does not produce degrading of the distance detecting accuracy due to background or foreground.
These objects are attained by providing a distance detecting device comprising: an optical system which forms an image of a photographic subject; an image sensor having a plurality of pixels which receive light flux from a photographic subject through said optical system; an extraction circuit which extracts image information of a specific region of said image sensor; a distance calculator which calculates the distance to a photographic subject from the image information of a region extracted by the extraction circuit; a detector which detects the posture of the distance detecting device; and a changer which changes a shape of the specific region in accordance with posture detected by the detector.
According to this construction, the light flux from a photographic subject passing through the optical system impinges the image sensor, and the shape of the measurement region is set on the image sensor in accordance with the posture of the distance detecting device when said posture is changed. The distance to a photographic subject is calculated by the distance calculator via the difference in the luminance distributions of the measurement regions.
The said specific region is longer in a vertical direction than a horizontal direction.
According to this construction, the measurement region is normally longer in a vertical direction than a horizontal direction when the posture of the distance detecting device is changed.